Light emitting diode (LED) lighting systems are becoming more widely used instead of traditional lighting. Light emitting diode lamps (an example of solid state lighting) can have advantages over traditional lighting such as the incandescent light bulb, halogen lighting, or fluorescent lighting, due to lower energy usage, increased stability and longer lifetimes, ability to be used in a wider variety of applications than fluorescent lighting, ability to be tuned to an exact color desired, among other reasons. In some embodiments, a single LED chip/die is within the lamp, and in other embodiments a plurality of LEDs is within the same lamp. The outer housing of an LED lamp can be made to the same specifications as an incandescent bulb, thus allowing use where incandescent bulbs are used.
Light emitting diodes (LEDs) are solid state devices that convert electric energy to light, and generally have at least one semiconductor material with n-doped and p-doped portions. Organic light emitting diodes are also known. When a bias is applied across semiconductor material, holes and electrons are injected into the active layer where they recombine to generate light. Light is emitted from the active layer and can be directed in primarily one direction, or in any direction, depending upon the type of LED.
LEDs can provide white light with a single LED, such as with a blue or violet LED that has a phosphor to shift the light closer to a perceived white light. LEDs may provide a single color (red, green or blue for example), or may be provided as different color LEDs in the same lamp which combine to provide white light. Examples of LEDs may include red LEDs using GaAsP and green LEDs using GaP, as well as nitride semiconductor LEDs that form green, blue or ultraviolet light. As LEDs become increasingly brighter, heat dissipation becomes an increasing concern, as heat build-up can degrade the LED performance.
Due to the desire for LED lamps to have high brightness and efficiency, passivation layers, adhesives and encapsulants preferably should be highly transparent to visible light.
Polymeric materials, including siloxane materials, are disclosed in US 2004010676, U.S. Pat. No. 6,984,483, US 20130165615 and U.S. Pat. No. 5,300,608.
There is still need for siloxane materials that can provide improved properties, such as at least one of transparency, low haze, low yellowing over time and low shrinkage, high durability and good thermal stability.